This frame was load-bearing, meaning that the steel skeleton would support the building's weight, not its walls.

VOA: special.2010.03.31

It's not going to be a backscatter event if your ping-pong ball hits the frame or these strings, or the top part.

打到原子核了就是背散射,如果打到框上。

麻省理工公开课 - 化学原理课程节选